Controllable synthesis of In-Plane Mo/Mo₂C heterojunction nanosheets for enhanced hydrogen evolution reaction

Two-dimensional (2D) molybdenum carbide (Mo₂C) is a potential electrocatalyst for the hydrogen evolution reaction (HER) due to its Pt-like electronic structure, high electrical conductivity, and abundant active sites. However, its practical application as an HER catalyst is hindered by the sluggish kinetics due to the strong hydrogen absorption. Herein, 2D in-plane Mo/Mo₂C heterojunction nanosheets are synthesized from bulk molybdenum disulfide (MoS₂) via a molten salt-assisted technique. The ultraviolet photoelectron spectra combined with density-functional theory (DFT) simulations elucidates that electrons are transferred from Mo to Mo₂C and fill Mo₂C antibonding orbitals, which weakens Mo-H bonding, enhances H₂O adsorption and dissociation, optimizes H adsorption/desorption of in-plane Mo/Mo₂C heterojunction nanosheets, thus promoting the HER kinetics. The Mo/Mo₂C heterojunction nanosheets electrocatalyst demonstrates exceptional HER performance with minimal overpotentials (90 mV in alkaline vs. 96 mV in acidic media at 10 mA cm^-2) and favorable Tafel slopes (54.9 vs. 64.2 mV dec^-1). Notably, it achieves a 280 mV overpotential at 500 mA cm^-2 under alkaline conditions, surpassing that of the commercial Pt/C electrode. The stability is excellent as confirmed by an increase of potential of only about 10 mV after operation for 100 h at 300 mA cm^-2. The results reveal a simple and effective strategy to boost the catalytic HER activity boding well for high-efficiency commercial water splitting.